A light emitting diode (LED) typically emits light with a Lambertian pattern such that the emitted light is spread over a large solid angle, rather than focused at a single spot. Consequently, many LED lighting products include an optical focusing mechanism. One common approach is to use a reflector system similar to a standard parabolic aluminized reflector (PAR) lamp or a parabolic cone surrounding the light source, as in a flashlight or a car headlight. The second approach is to use optical grade acrylic plastic refractive lenses. These are solid lenses with side surfaces positioned at angles to the LED that reflect most of the sideward light in the same forward direction as the rest of the light creating a focused beam. These are often referred to as TIR (total internal reflection) lenses.
LED reflector systems typically use aluminum applied through vapor deposition for the reflective surfaces because other more reflective surfaces degrade when exposed to the atmosphere. Generally, these reflector systems tend to be large because the light is aggregated by a single reflector in order to meet cost objectives. In these configurations, an LED array or multiple discrete LEDs are directed into a single light column. In contrast, the refractive lens solutions are more compact, however there are inherent losses associated with transmission of light through the surfaces of the lenses because the surface angles cannot reflect all incoming rays from the Lambertian output of the LEDs. In both cases, optical efficiencies are in the 75-85% range.
The foregoing examples of the related art and limitations are intended to be illustrative and not exclusive. Other limitations of the related art will become apparent upon a reading of the specification and a study of the drawings.